"The Iranian regime has a choice: it can either do a 180-degree turn from its outlaw course of action and act like a normal country, or it can see its economy crumble", Secretary of State Mike Pompeo told reporters.
As sanctions returned on Monday, Iran struck a defiant tone, with President Hassan Rouhani saying in a televised speech "I announce that we will proudly bypass your illegal, unjust sanctions because it's against global regulations".
"[The] Treasury's imposition of unprecedented financial pressure on Iran should make clear to the Iranian regime that they will face mounting financial isolation and economic stagnation until they fundamentally change their destabilizing behavior", Mnuchin said.
USA sanctions permit trade in humanitarian goods such as food and pharmaceuticals, but measures imposed on banks and trade restrictions could make such items more expensive.
Iranian state television aired footage of air defence systems and anti-aircraft batteries in two-day military manoeuvres which got under way across a vast stretch of the country's north. "We said that our economy should not be impacted by your policies", sources said.
Democratic Senator Tom Udall, who is also a member of the Senate Foreign Relations Committee, said, "Led by people like John Bolton, who believe that we should bomb Iran, I fear the Trump administration is marching toward another catastrophic war in the Middle East". "We stand with them as they call for the regime to respect their human rights and dignity", said US Special Representative for Iran, Brian Hook.
"We are in the war situation", President Hassan Rouhani said in a television address as the sanctions snapped into place.
But as the administration seeks to cut off Iran's oil revenue it will allow some of its closest allies and rival China to continue to purchase Iranian oil as long as they work to reduce imports to zero.
"A waiver was granted to allow Iraq to continue to pay for electricity imports from Iran", a State Department official told Al-Monitor. He said the pressure "is only going to mount from here" unless Iran's leaders halt its support for terrorism and abandon its nuclear ambitions "immediately".
"These exemptions are premised on significant reductions of Iranian oil imports by countries such as China and Turkey when there is minimal evidence of such reductions".
China, which has been Trump's main sparring partner on the trade front, is Iran's main oil customer.
"Resistance is not just a concept exclusive to Iranians - although we like this concept and we focus on it".
Sajjadpour's said his country remained confident that it would survive the latest setback, nearly 40 years since the Iranian revolution, and had endured significantly harsher circumstances in periods such as during the Iran-Iraq war in the 1980s. "We must resist and win", he said.
The Iranian official insisted the country had cooperated fully in the implementation of the JCPOA, but could not tolerate having to abide by the agreement but also endure sanctions.
Iran's clerical rulers dismissed the curbs. The United States said on November 2 it will temporarily allow eight importers to keep buying Iranian oil.
Foreign companies and banks are largely unwilling to make enemies of the US Treasury, and most worldwide firms that set up in Iran after the 2015 deal have been forced to leave, including France's Total, Peugeot and Renault, and Germany's Siemens.
He said the Iranian economy was struggling because of the government's "negligence of its own people".